The major objective of this project is to delineate psychosocial, behavioral, contextual, and biological vectors of vulnerability to smoking initiation and maintenance in adolescents and young adults. Psychological dispositions such as impulsivity, hostility, and negative affectivity are associated with elevated rates of tobacco use, but little is known about how these traits influence smoking initiation during the adolescent and young adult periods or how they interact with family and peer contexts, situational influences, nicotine reactivity, and genetic makeup to enhance or impede the progression toward regular smoking. A related aim is to identify developmental trajectories for stages of smoking at the two highest risk ages for tobacco use onset: early adolescence and young adulthood. In Study l, 120 14-year old adolescents and 120 college freshmen (40 at each age in each of 3 smoking stages: never, experimental, regular) will be signaled twice each hour to complete diaries that include information about their location, activities, social context, mood, stress levels, consummatory behaviors, and urges to eat and smoke. Self-reports of cigarette use will be validated by analyses of salivary cotinine. This 4-day ambulatory recording sequence will be repeated twice each year for 4 consecutive years to provide information about developmental trajectories. We will also assess the role of gender and specific trait and behavioral characteristics in these relationships. Study 2 will examine the influence of estrogen levels on these relationships by comparing cue-reactivity and nicotine effects during the luteal vs. the follicular menstrual phases. Secondary goals include (a) examination of the moderating role of situation-behavior phenotypes on associations between specific candidate genes and tobacco use, and (b) comparisons of smoking phenotypes across the adolescent, young adult, and middle adult years. Consistent with the transdisciplinary approach, this project focuses simultaneously on several disciplinary levels of analysis (environmental, psychosocial, behavioral, neurobiological) using a shared conceptual framework. interactive links among the projects in this Center include the use of the behavior-context profiles or phenotypes identified in this project to help guide brain imaging studies- and elucidate the brain activation patterns that emerge from Project 2, and to inform the targeted antismoking strategies to be developed in Project 4.